The present invention relates to observation of logic circuitry, and in particular to use of serial scan techniques to perform a real-time observation of the logic circuitry without the need of interrupting normal logic operation.
There are available today are a number of techniques for testing digital logic circuitry, but many if not all require normal operation to be interrupted for the test to proceed. There are also fault-tolerant designs that incorporate error checking circuitry for ensuring proper operation, and to halt operation or take some other action if an error is detected. Often, however, there are times when a digital system may not encounter an error, may be in proper operating condition, but stuck in an operating (e.g., hardware) loop, or hung, unable to exit. It is this type of condition that needs detection.
Thus, there is a need, not necessarily for testing a digital system, but merely to provide real-time observation of the on-going operation of the system to ensure that the system is operating correctly without interrupting operation of the system.